This invention relates generally to sampling apparatus for gathering a representative sample of flowing material and more particularly, but not by way of limitation, to an automatic sampling apparatus that obtains a full cross-sectional sample within a positively or negatively pressurized (i.e., above or below atmospheric pressure) pipe or duct system.
In blending processes, there is the need for sampling mixed or blended materials, whether the blends are of solids or liquids or a mixture of solids and liquids or a mixture of solids and gases, to know the amounts of the constituent components for controlling quality of the ultimate blend. For example, in making a cement slurry for use during a cementing job at an oil or gas well, the operator of the job needs to monitor the constituents of the blend to insure that the resultant cement slurry has the necessary properties for the particular job. This need is particularly critical when the blend may have segregated layers of constituent elements so that the blend is not homogeneous. In such a case, a full cross-sectional sample of the blend should be taken to obtain portions of all the layers.
Because some blends are conveyed under pressure, such as in a pneumatic flow, there is the further need for such a full cross-sectional sampling to be taken even in such a pressurized environment, thereby necessitating a suitable sealed construction to prevent loss of material and pressure from within the system. That is, there is the need for an apparatus including a sealing structure which allows the sample of material to pass out of the primary flow path without unwanted loss of material or pressure. The need for a sealing structure also exists when the sampling is taken in a negatively pressurized environment, such as in a vacuum conveyance system.
Several automatic sampling apparatus have been marketed or contemplated. Some are for gravity-flow systems and others are for pressurized systems. Some utilize a sample-taking element fixed in the flow stream and others utilize retractable elements. Some elements are movable across the flow path to take a full cross-sectional sample, but these are not known to be for use in above-atmospheric or below-atmospheric pressure systems. Additionally, at least one of these incorporates a scoop-like element which effectively impedes or otherwise adversely affects the primary flow. Another has a diverting flow line incorporating valves and actuators to open an alternate flow path through which to collect a sample; this type is relatively expensive because of the valves and actuators required, and it is also difficult to clean.
Despite these other types of automatic material samplers, we believe there is a need for an automatic sampling apparatus which can take a full cross-sectional sample of a material flowing under a greater or less than atmospheric pressure without significantly adversely affecting the primary flow, whereby more accurate and reliable samples can be collected from such a a pressurized flow system. Such accuracy and reliability are particularly important where the samples are being used to monitor flows within systems for producing complex blends, such as for producing complex cement slurries at a well site. Improved accuracy and reliability would, in general, provide an important competitive advantage. Such improved sampling makes the blending process more cost effective. To further enhance the cost effectiveness, it is desired that such an apparatus which meets the aforementioned needs also be less expensively constructed than previously known types of sampling apparatus.